Drying apparatus

ABSTRACT

The invention provides drying apparatus ( 10; 100; 200; 300 ) comprising a first chamber ( 32; 132; 232; 332 ) for receiving articles to be dried and having an outlet ( 38; 138; 238 ), a second chamber ( 26;126; 226;326 ) having an outlet ( 28   a   ; 128; 228; 328 ), and a fan ( 40; 140; 240; 340 ) having a fan inlet and a fan outlet, the fan inlet communicating with the outlet ( 38; 138; 238 ) of the first chamber ( 32; 132; 232; 332 ) and the fan outlet communicating with the second chamber ( 26;126; 226; 326 ), the apparatus ( 10; 100; 200; 300 ) further comprising a vacuum pump ( 30; 130; 230; 330 ) communicating with the outlet ( 28   a   ; 128; 228; 328 ) of the second chamber ( 26;126; 226; 326 ), the arrangement being such that transfer of thermal energy can take place between the first and second chambers ( 32, 26; 132,126; 232, 226; 332, 326 ). The invention also provides a method of drying articles comprising the steps of: (a) placing the articles into a first chamber ( 32; 132; 232; 332 );(b) evacuating a significant proportion of the air from the first chamber ( 32; 132; 232; 332 ) and from a second chamber ( 26;126; 226; 326 );(c) evacuating water vapour from the first chamber ( 32; 132; 232; 332 ) to the second chamber ( 26;126; 226; 326 );(d) allowing the water vapour to condense in the second chamber ( 26;126; 226; 326 ); and (e) transferring thermal energy from the second chamber ( 26;126; 226; 326 ) to the first chamber ( 32; 132; 232; 332 ).

[0001] The invention relates to drying apparatus and to a method ofdrying articles. Particularly, but not exclusively, the inventionrelates to domestic drying apparatus for drying laundry articles orkitchenware and crockery and to a method suitable for use in a domesticenvironment.

[0002] Conventional methods of drying laundry articles involve tumblingthe articles in a drum whilst a warm airstream is passed therethrough.The water trapped in the articles evaporates into the warm airstream andis carried out of the drum therewith. The water vapour is eitherreleased into the atmosphere or condensed out of the airstream andcollected to be drained off. Conventional methods of drying articles ina dishwasher device also involve passing heated air over the articles tocause evaporation of the water lying on the articles and removing thewater vapour with the airstream. The disadvantages of these methodsinclude the fact that the articles to be dried are often subjected tohigh temperatures if a particularly fast drying time is required. In thecase of clothes dryers, this can damage the fabric and, in the case ofdishwashers, the crockery becomes too hot to handle as soon as thewashing and drying cycle has finished.

[0003] It is a well known principle that water will boil at atemperature lower than 100° C. if the pressure in the vessel in which itis contained is reduced below atmospheric. Proposals for drying laundryarticles based on this principle have been put forward but, to date,none has been found to be sufficiently effective to form the basis for acommercially-viable drying apparatus. The principal reason for this isthat the vacuum pump by means of which the chamber containing thearticles to be dried is evacuated is required to deliver very high flowrates, in order to be able to evacuate the evaporating water vapour, andto develop a high pressure drop thereacross. Such components, whilstavailable on the market, are prohibitively expensive for use in thecontext of domestic apparatus.

[0004] It is therefore an object of the present invention to providedrying apparatus capable of operating on the principle of reducedpressure so as to evaporate water vapour from articles at a temperaturelower than 100° C. and which is more cost-effective than previouslyproposed arrangements. It is another object of the invention to providedrying apparatus which is suitable for use in the domestic environment.It is a further object of the invention to provide a method of dryingarticles based on the principle of reduced pressure so as to evaporatewater vapour from articles at a temperature lower than 100° C. which ismore cost-effective than previously proposed methods. It is a stillfurther object of the invention to provide a method of drying articleswhich is suitable for use in the domestic environment.

[0005] The invention provides drying apparatus comprising a firstchamber for receiving articles to be dried and having an outlet, asecond chamber having an outlet, and a fan having a fin inlet and a fanoutlet, the fan inlet communicating with the outlet of the first chamberand the fan outlet communicating with the second chamber, the apparatusfurther comprising a vacuum pump communicating with the outlet of thesecond chamber, the arrangement being such that transfer of thermalenergy can take place between the first and second chambers and meansare provided for causing forced circulation of water vapour containedwithin the first chamber.

[0006] The arrangement provided avoids the need to provide a vacuum pumpcapable of developing a high pressure drop and delivering a high flowrate. Essentially, the arrangement allows the first and second chambersto be evacuated after which the water vapour evaporated in the firstchamber is condensed in the second chamber without being passed throughthe vacuum pump. Hence the vacuum pump is required to deliver only arelatively small volume of gas. As such, the cost of the components iskept to a minimum.

[0007] The arrangement also takes advantage of the fact that, when thewater evaporates in the first chamber, it absorbs energy which, in theabsence of any input of energy, causes a drop in temperature. Similarly,when the water vapour condenses in the second chamber, it releasesenergy. However, if the temperature in the first chamber dropssignificantly, the pressure reduction therein will need to be greater toensure that the water in the articles is evaporated. Thus, the transferof thermal energy from the second chamber to the first chamber maintainsthe temperature in the first chamber and allows the pressure in bothchambers to be maintained at an achievable value without reducing therate at which water can be evaporated in the first chamber.

[0008] An advantage provided by the invention, when used in the field ofclothes dryers, is that effective drying can be carried out relativelyquickly without subjecting the articles to be dried to excessively hightemperatures. When used in the field of dishwashers, a similar advantageis that, at the end of the washing and drying process, the crockery andkitchenware are at a temperature which is not too hot to be handledimmediately.

[0009] In a preferred arrangement, the first and second chambers have atleast one common wall, with the or each common wall being thermallyconductive. If the common wall is thermally conductive, it will remainat a lower temperature than the second chamber and so provide a surfaceon which the water vapour will readily condense. Also, the latent heatof condensation will then pass through the thermally conductive wallinto the first chamber to maintain the temperature therein and soencourage the water therein to evaporate from the articles. Thisincreases the efficiency of the apparatus as a whole.

[0010] Preferably, the first chamber is located partially, morepreferably wholly, inside the second chamber. Such an arrangementmaximises the area of the common wall available to the water vapour forcondensation purposes.

[0011] It is also preferable, at least for applications in the laundryfield, if the first chamber is mounted so as to be rotatable about anaxis and means are provided for causing the first chamber to rotateabout the axis. In an alternative embodiment, the first chamber maycomprise an outer housing and an inner drum, with the outer housingbeing held stationary with respect to the second chamber and the innerdrum being mounted so as to be rotatable with respect to the outerhousing. In either case, the articles (which will be articles oflaundry) can be tumbled within the first chamber so that differentportions of the articles are caused to come into contact with thechamber or drum during the drying process. This reduces the risk of thearticles being dried in some places and not others.

[0012] The alternative embodiment mentioned above can also include atleast one vane or blade for causing circulation of air or water vapourwithin the first chamber when the drum is caused to rotate. Thisencourages the water vapour to pass across and through C the articles tobe dried and maximises evaporation of the water within the firstchamber.

[0013] It is preferred that the apparatus is a clothes dryer or adishwasher.

[0014] The invention also provides a method of drying articlescomprising the steps of

[0015] (a) placing the articles into a first chamber;

[0016] (b) evacuating a significant proportion of the air from the firstchamber and from a second chamber;

[0017] (c) evacuating water vapour from the first chamber to the secondchamber;

[0018] (d) allowing the water vapour to condense in the second chamber;

[0019] (e) transferring thermal energy from the second chamber to thefirst chamber; and

[0020] (f) causing forced circulation of the air and/or water vapourcontained within the first chamber.

[0021] By transferring thermal energy from the second chamber to thefirst chamber, the method minimises energy consumption whilst maximisingwater evaporation in the first chamber. The power consumption requiredto operate the vacuum pump is also minimised.

[0022] In a preferred embodiment, the articles are tumbled or otherwiseagitated during at least part of the drying process. This maximises thearea of contact of the articles with a surface which is at a relativelyhigh temperature and thus reduces the risk of areas of the articlesremaining wet or damp.

[0023] Preferably, the air and/or water vapour in the first chamber isforced to circulate therein, more preferably through the articlesthemselves, so as to improve the removal, by evaporation, of water whichmight otherwise remain trapped within the articles.

[0024] Embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings, wherein:

[0025]FIG. 1 is a schematic side sectional view through a firstembodiment of the invention;

[0026]FIG. 2 is a schematic side sectional view through a secondembodiment of the invention;

[0027]FIG. 3a is a schematic side sectional view through a thirdembodiment of the invention;

[0028]FIG. 3b is a transverse sectional view of the embodiment shown inFIG. 3a taken along the line III-III;

[0029]FIG. 4a is a schematic side sectional view through a fourthembodiment of the invention; and

[0030]FIG. 4b is a transverse sectional view of the embodiment shown inFIG. 4a taken along the line IV-IV.

[0031] A first embodiment of the invention is illustrated in FIG. 1. InFIG. 1, the drying apparatus according to the invention takes the formof a dishwasher 10. The dishwasher 10 comprises an outer casing 12having an upper wall 12 a, side walls 12 b and a base 12 c. Suspendedbetween the side walls 12 b and sealingly attached thereto, is a tray 14which is inclined downwardly towards an outlet 16. The outlet 16 isconnected to a discharge pipe 18 which leads out of the dishwasher 10and includes means (not shown) for connecting the discharge pipe 18 to asuitable drain for removing waste water from the dishwasher 10. A pump20 and a one-way, non-return valve 22 are arranged between the outlet 16and the discharge pipe 18 for reasons which will be explained below. Thepump 20 and the non-return valve 22 are located and housed in a lowerchamber 24 delimited by the tray 14, the base 12 c and the lowerportions of the side walls 12 b.

[0032] An upper chamber 26 is delimited by the tray 14, the upper wall12 a and the upper portions of the side walls 12 b. This upper chamber26 is manufactured so as to be substantially airtight. Appropriatemanufacturing and sealing techniques will be apparent to a skilledreader. A first outlet 28 a communicates with the interior of the upperchamber 26 and leads to a vacuum pump 30 of the type which is capable ofdeveloping a relatively high pressure drop (say, 70-90 kPa) anddelivering a relatively low flow rate (say, 0.5-1.0 l/s). A secondoutlet 28 b also communicates with the interior of the upper chamber 26and incorporates a valve 31 which allows the second outlet 28 b to beclosed or opened as required. The first and second outlets 28 a, 28 beach lead, beyond the vacuum pump 30 or the valve 31, to an appropriatelocation for discharging evacuated air from the dishwasher 10. It isenvisaged that this location could be simply to atmosphere.

[0033] Located inside the upper chamber 26 is an inner chamber 32. Theinner chamber 32 is sealed in an airtight manner from the upper chamber26. The inner chamber 32 houses various items of racking 34 adapted andarranged to receive items of kitchenware and crockery 36 to be washedand dried by the dishwasher 10. The inner chamber 32 has an outlet 38connected directly to the inlet of a blower 40. The blower 40 isconnected to a motor 42 for driving the blower 40. The blower 40 is of atype which is capable of passing a relatively high volume of air persecond (say, 12-45 l/s) and discharges directly into the upper chamber26. A heater 44 is located in the inner chamber 32 immediately beneath,or directly in contact with, the lowermost racking item 34 for purposeswhich will be described below.

[0034] The inner chamber 32 is located wholly within the upper chamber26. Hence, the walls of the inner chamber 32 form the innermostboundaries of the upper chamber 26. The walls of the inner chamber 32are thus common to both the inner chamber 32 and the upper chamber 26.The walls of the inner chamber 32 are made from a suitable metal orother thermally-conductive material.

[0035] It will be understood that the dishwasher 10 will furthercomprise known components required for effecting a washing action. Thecomponents described above are required in order to effect drying of thekitchenware and crockery 36 which have previously been washed in thedishwasher 10. However, further description of the components requiredto carry out the washing process will not be described any further here.

[0036] The drying operation of the dishwasher 10 will now be described.Following the completion of the washing cycle, a significant quantity ofwater will remain inside the inner chamber 32, particularly on thesurfaces of the kitchenware and crockery 36. The temperature of thecontents of the inner chamber 26 is likely to be in the region of 20° C.A drying process is required in order to complete the washing and dryingprocess. In order to achieve this, the blower 40 is operated so as todraw air from the inner chamber 32 into the upper chamber 26 at arelatively high rate. The valve 31 is also opened so that the air in theupper chamber 26 is emitted from the dishwasher 10. This occurs as aresult of the increase in pressure in the upper chamber 26 whichinevitably. occurs when air is drawn from the inner chamber 32 by theblower 40 and. passed to the upper chamber 26. When a significantproportion of the air in the inner chamber 32 has been removed therefromby the blower 40, the valve 31 is closed. If desired, the blower 40 canbe turned off so that the pressures within the inner and upper chambers32, 26 can be allowed to equalise. The blower 40 is then reactivated andthe valve 31 opened again so as to allow more air to be expelled fromthe upper chamber 26. This process can be repeated several times ifdesired. At the end of this process, the valve 31 is closed, and thevacuum pump 30 is activated so as to evacuate the upper chamber 26 to apressure which is significantly lower than atmospheric. By this method,a pressure of around 10 kPa should be achievable within the innerchamber 32 in a relatively short space of time. The water containedwithin the inner chamber 32 will remain in liquid form at this pressureand at a temperature of around 20° C.

[0037] Once the desired reduced pressure has been achieved, the heater44 is turned on. This causes the temperature inside the inner chamber 32to rise which, in turn, causes the water to evaporate at a temperaturewhich is much lower than 100° C. The temperature at which the waterbegins to boil will depend upon the pressure of the air inside the innerchamber 32. In the embodiment, it is envisaged that the temperatureinside the inner chamber 32 will be raised to around 50° C. As the waterin the inner chamber 32 begins to evaporate, the blower 40 removes thewater vapour from the inner chamber 32 and transfers it to the upperchamber 26. However, the transfer of the water vapour from the innerchamber 32 to the upper chamber 26, which is at a higher pressure thanthe inner chamber 32, encourages condensation of the water vapour. Thewater vapour thus condenses on the walls of the inner chamber 32.

[0038] It will be understood that, when the water evaporates in theinner chamber 32, it absorbs energy and the tendency will be for thetemperature inside the inner chamber 32 to drop below the desiredtemperature of 50° C. Also, as the water vapour condenses in the upperchamber 26, its latent heat of condensation is given out, thus causing arise in temperature in the upper chamber 26. In the steady state,therefore, the temperature of the water vapour in the upper chamber 26will be greater than the temperature in the inner chamber 32 and therewill be a temperature differential across the walls of the inner chamber32, which are in fact common to both chambers 26,32. This allows thermalenergy to pass back through the walls of the inner chamber 32 from theupper chamber 26 into the inner chamber. This transfer of thermal energyhelps to prevent the temperature inside the inner chamber 32 fromdropping to a very low temperature without the continued application ofheat from the heater 44. If no heat were transferred into the innerchamber 32, the temperature would drop back to a comparatively low value(say, 20° C) and there would be no further evaporation of water at theselected pressure inside the inner chamber 32. A further reduction inthe pressure inside the inner chamber 32 would be required if anyfurther evaporation were to take place. If the pressure droprequirements are too great, then the vacuum pump 30 will need to becapable of developing a very high vacuum and apparatus of this sort isgenerally very expensive.

[0039] In the steady state, therefore, the blower 40 and vacuum pump 30are operating, the valve 31 is closed and the heater 44 is either off oractivated on a very low output. The pressure inside the inner chamber 32will be lower than that in the upper chamber 26 and the temperatureinside the inner chamber 32 will be lower than that in the upper chamber36. There will be a temperature differential across the walls of theinner chamber 32. In one example of the apparatus illustrated above, theestimated steady-state pressure inside the inner chamber 32 isapproximately 12-14 kPa and the temperature therein will beapproximately 50° C. In the upper chamber 26, the pressure will beapproximately 20-25 kPa and the temperature will be approximately 60-65°C. In the inner chamber 32, whilst liquid water remains therein, waterwill continue to evaporate and the water vapour will be extractedtherefrom and passed to the upper chamber 26. The water vapour willcondense on the walls of the inner chamber 32, from where it will fallonto the tray 14 and be collected at the outlet 16. At the end of thewashing(ringing cycle, the pump 20 is operated in order to remove thecondensed water from the dishwasher 10. If required, the condensed watercan be stored for use in a subsequent dishwashing cycle.

[0040] A second embodiment of apparatus according to the invention isillustrated in FIG. 2. In this embodiment, the apparatus takes the formof a tumble dryer or clothes dryer 100. The clothes dryer 100 has anouter casing 112 which may be generally cylindrical in shape. The outercasing 112 has a cylindrical wall 112 a, a rear wall 112 b and a door112 c arranged opposite the rear wall 112 b. The door 112 c is hinged soas to be openable so as to allow access to the interior of the clothesdryer 100. Appropriate seals are provided around the door 112 c in orderto allow the interior of the clothes dryer 100 to be evacuated as willbe described below. The lower portion of the cylindrical wall 112 a isshaped in the manner of a sump 114 and inclined towards an outlet 116.As described above, the outlet 116 is connected to a discharge pipe 118with a pump 120 located therebetween and a one-way, non-return valve 119located in the discharge pipe 118.

[0041] An outer chamber 126 is defined and delimited by the outer casing112. An outlet 128 communicates with the outer chamber 126 and with aone-way, non-return valve 129 and a vacuum pump 130 located in theoutlet 128. A spur outlet 128 a communicates with the outlet 128 and hasa valve 131 located therein. As before, both the outlet 128 And the spuroutlet 128 a lead to a location (not shown) at which air evacuated fromthe clothes dryer 100 can be safely and easily released, eg. into theatmosphere. Inside the outer chamber, a cylindrical inner chamber 132 isprovided. The inner chamber 132 has a cylindrical wall 132 a, a rearwall 132 b and a door 132 c located opposite the rear wall 132 b. Sealsare provided around the door 132 c which will allow the inner chamber132 to be evacuated to a pressure lower than that of the outer chamber126. The inner chamber 132 is located within the outer chamber 126 sothat the doors 112 c, 132 c are substantially aligned This allows bothdoors 112 c, 132 c to be opened in order to allow articles of laundry tobe introduced to the interior of the inner chamber 132 so that thedrying process can be carried out.

[0042] Mounted on the rear wall 132 b of the inner chamber 132 are aplurality of blowers 140 and motors 142. The blowers 140 and motors 142are equispaced about the axis 136 so that the mass of these componentsis balanced. Apertures 138 are provided in the rear wall 132 b adjacenteach blower 140. The apertures 138 form outlets from the inner chamber132 so that water vapour can be evacuated from the inner chamber 132 andtransferred into the outer chamber 126 via the blowers 140. Each blower140 discharges water vapour directly into the outer chamber 126. Alsoprovided on the cylindrical wall 132 a is a heating element 144,preferably in the form of a film heater wrapped around the cylindricalwall 132 a, appropriate insulation (not shown) being provided ifrequired.

[0043] The inner chamber 132 is supported on a shaft 134 which, in turn,is rotably mounted, by means of bearings 134 a, on the rear wall 112 bof the outer casing 112. A motor 134 b is provided so that when themotor 134 b is activated, the inner chamber 132 is caused to rotateabout its longitudinal axis 136. The axis 136 may be, but need not be,coincident with the longitudinal axis of the cylindrical wall 112 a ofthe outer casing 112.

[0044] It will be appreciated that an appropriate electrical connectionwill need to be provided to the motors 142 so as to allow the innerchamber 132 to rotate about the axis 136. An electrical connection tothe heating element 144 will also be required. Such rotatableconnections are available but can be replaced, if desired, by otherarrangements by means of which water vapour can be evacuated from theinner chamber 132 into the outer chamber 126 whilst the inner chamber132 is rotating about the axis 136.

[0045] The clothes dryer 100 described above operates as follows.Articles of laundry requiring to be dried are introduced to the interiorof the inner chamber 132 via the doors 112 c, 132 c. Thereafter, thedoors 132 c, 112 c are closed. The blowers 140 are then operated withthe valve 128 a open so as to evacuate air from the inner chamber 132into the outer chamber 126 and thence to atmosphere. When the majorityof the air has been evacuated from the inner chamber 132, the valve 131is closed and the vacuum pump 130 is operated so as to evacuate theouter chamber 126 to a pressure of between 20 and 25 kPa. The heater 144is then turned on so as to raise the temperature of the contents of theinner chamber 132. As the temperature of the contents of the innerchamber 132 is being raised, the motor 134 b is operated so as to causethe inner chamber 132 to rotate about the axis 136. If the speed ofrotation is above that at which the laundry articles are held againstthe cylindrical wall 132 a of the inner chamber 132, heat will bereadily and easily passed from the cylindrical wall 132 a to the laundryarticles. At a speed lower than that at which the laundry articles willremain held against the cylindrical wall 132 a, the laundry articleswill be tumbled inside the inner chamber 132. This maximises theopportunity for the water droplets trapped within the laundry articlesto be released into the low pressure atmosphere within the inner chamber132. Periods of rotation at a speed which causes tumbling orredistribution of the laundry articles inside the inner chamber 132,ideally no more than 50 rpm, can be alternated with periods of rotationat a higher speed whilst the temperature of the contents of the innerchamber 132 is increased to the desired temperature.

[0046] Water droplets trapped within the fibres of the laundry articleswill begin to evaporate inside the inner chamber 132 as the temperaturewithin the inner chamber 132 increases. The temperature at which thewater droplets will evaporate will depend upon the pressure inside theinner chamber 132. Spinning the inner chamber 132 at a high speed canalso help to extract water from the laundry articles. The blowers 140remain activated as the water evaporates so as to move the water vapourfrom the inner chamber 132 into the outer chamber 126. The compressionof the water vapour as it passes through the blowers 140 and enters theouter chamber 126 encourages condensation on the walls of the innerchamber 132. The condensed water collects in the sump 114 and isdischarged through the outlet 116 and discharge pipe 118 by way of thepump 120.

[0047] The cylindrical wall 132 a of the inner chamber 132 ismanufactured from a thermally-conductive material so that, aspreviously, at least some of the latent heat of condensation given offby the condensing water vapour is transferred through the cylindricalwall 132 a into the inner chamber 132. This heat energy is passed to thelaundry articles in the inner chamber 132. Continued rotation of theinner chamber 132 discourages localised warming and also allows water tobe evaporated from all areas of the laundry articles. In this way,different areas of the laundry articles come into contact with thewarmed cylindrical wall 132 a of the inner chamber 132 at differenttimes.

[0048] A particular advantage of the arrangement illustrated above isthat of being able to detect when the drying process is complete. Whilstwater remains present in the inner chamber 132, the water will continueto evaporate in an ongoing manner. Hence, although the blowers 140continue to remove water vapour from the inner chamber 132, the pressuretherein will remain relatively constant. However, once substantially allof the water has evaporated, continued operation of the blowers 140 willcause a reduction in the pressure inside the inner chamber 132. A simplepressure detector 146 located inside the inner chamber 132 can thereforebe used to give an indication that the drying process is essentiallycomplete. Alternatively, a sensor (not shown) can be provided to detecta significant increase in the speed of the blower 140 and/or a reductionin the power absorbed by the blower 140. This can also be used toprovide An indication that the drying process is complete.

[0049] The third embodiment illustrated in the drawings is a variationon the second embodiment illustrated in FIG. 2. Figure la is a schematicside view of the third embodiment, similar to the side view shown inFIG. 2, and FIG. 3b is a sectional view through the apparatus shown inFIG. 3a.

[0050] The outer chamber of the clothes dryer 200 illustrated in FIGS.3a and 3 b is very similar to that shown in FIG. 2 and described above.Hence, the clothes dryer 200 has an outer casing 212 having acylindrical wall 212 a, a rear wall 212 b and a door 212 c locatedopposite the rear wall 212 b. As before, the door 212 c is sealed in anairtight manner against the remainder of the outer casing 2.12 when itis closed. The outer casing 212 has a sump 214 in the lower regionthereof, which sump 214 has an outlet 216 leading to a discharge pipe218 via a pump 220. The outer casing 212 delimits the outer chamber 226which communicates with an outlet 228 leading to a vacuum pump 230 and aspur outlet 228 a incorporating a valve 231. Thus far, the features ofthe clothes dryer 200 are the same as the corresponding features of theclothes dryer 100 illustrated in FIG. 2.

[0051] The clothes dryer 200 also has an inner chamber 232 locatedinside the outer chamber 226. However, in contrast to the rotatableinner chamber 132 of the clothes dryer 100, the inner chamber 232 of thepresent embodiment is rigidly mounted inside the outer chamber 226. Theinner chamber 232 has a cylindrical wall 232 a, a rear wall 232 b and adoor 232 c located remote from the rear wall 232 b. As before, the door232 c is sealed against the remainder of the inner chamber 232 in anairtight manner when it is closed. A blower 240 is mounted close to therear wall 232 b of the inner chamber 232. A motor 242 is provided inorder to power the blower 240. A conduit 238 leads from the rear wall232 b to the blower 240 for carrying gas (water vapour) from theinterior of the inner chamber 232 to the blower 240 when the motor 242is activated. The outlet of the blower 240 leads to a three way valve243 which is able to direct gas leaving the blower 240 along one of twopassageways. The first passageway 243 a opens into the outer chamber226. The second passageway 243 b leads back into the inner chamber 232and has a heating element 244 coiled thereabout. The heating element 244can be used to warm the gas passing along the second passageway 243 b.

[0052] Mounted inside the inner chamber 232 is a rotatable drum 250. Thedrum 250 has a perforated cylindrical wall 252 a and a circular rearwall 252 b which can also be perforated if desired. An inwardlyextending lip 252 c surrounds the edge of the cylindrical wall 252 a onthe side remote from the rear wall 252 b. The drum 250 is located insidethe inner chamber 232 so that the opening defined by the lip 252 c issubstantially in line with the door 232 c of the inner chamber 232.

[0053] A shaft 234 is rigidly attached to the rear wall 252 b of thedrum 250. The shaft 234 is rotatably mounted by way of bearings 234 a onthe rear wall 232 b of the inner chamber 232. A motor 234 b is providedto enable the drum 250 to be rotated about the axis 236. The axis 236 iscoincident with the longitudinal axis of the drum 250 and preferablyalso coincident with the longitudinal axis of the inner chamber 232.

[0054] As has been previously mentioned, the cylindrical wall 252 a ofthe drum 250 is perforated. The perforations are sufficiently small toretain the laundry items to be dried inside the drum 250. The lip 252 calso assists in retaining the laundry articles in the interior of thedrum 250 when it is rotated about the axis 236 on actuation of the motor234 b. The door 323c is located and arranged so as to retain the laundryarticles inside the drum 250.

[0055] A plurality of vanes 254 are arranged on the external surface ofthe cylindrical wall 252 a of the drum 250. The vanes 254 extend axiallyalong the length of the drum 250, parallel to the axis 236. As can beseen in FIG. 3b, each vane 254 is curved in profile.

[0056] As the drum 250 is caused to rotate the vanes 254 bring aboutforced circulation of the water vapour present within the inner chamber232 and it is preferred that their shape and profile will be selected soas to effect good circulation within the inner chamber 232.

[0057] In operation, as before, the laundry articles to be dried areplaced inside the drum 250. The doors 212 c and 232 c are used toachieve this. Once the doors 212, 232 c have been closed, the blower 240is activated so as to remove air from the interior of the inner chamber232, In order to achieve this, the three way valve 243 is set so as topass the incoming air along the first passageway 243 a, ie the air isremoved from the inner chamber 232 and passed into the outer-chamber226. The valve 231 is open to allow the air removed from the innerchamber 232 to be discharged from the dryer 200. Once the majority ofthe air has been removed from the inner chamber 232 in this way, thevalve 231 is closed and the vacuum pump 230 is actuated so that theouter chamber 226 and the inner chamber 232 are both evacuated.

[0058] At this stage, the three way valve 243 is switched to a positionin which gas leaving the blower 240 is directed along the secondpassageway 243 b and the heating element 244 is turned on. The gas nowmoved by the blower 240 will simply be circulated through the blower andalong the second passageway 243 b, thus causing the said gas to bewarmed by the heating element 244. The temperature of the contents ofthe inner chamber 232 thus rises and the water contained within theinner chamber 232 will, at a temperature dependent upon the pressurewithin the inner chamber 232, begin to evaporate. When the desiredtemperature of the inner chamber 232 has been reached, the three wayvalve 243 is returned to the position in which water vapour leaving theblower 240 is passed to the outer chamber 226. Hence the blower 240 willremove the water vapour from the inner chamber 232 to the outer chamber226. Because of the inevitable temperature difference between the innerchamber 232 and the outer chamber 226, the water vapour condenses in theouter chamber 226, most probably on the outer wall of the inner chamber232, giving out the latent heat of condensation as condensation takesplace and causing the wall of the inner chamber 232 to become warmed.The condensed water will collect in the sump 214 and be removedtherefrom via the outlet 216 and the discharge pipe 218 using the pump220.

[0059] In order to ensure that all parts of the laundry articles areexposed to air and water vapour during this process, the drum 250 inwhich the laundry articles are contained is rotated about the axis 236.This is brought about by actuation of the motor 234 b which causesrotation of the shaft 234 and thus rotation of the drum 250. The speedof rotation of the drum 250 is such that the laundry articles perform atumbling action inside the drum 250.

[0060] In order to further enhance the ability of the above-describedapparatus to remove all water droplets from the laundry articles, meansare provided for forcing the water vapour, and any remaining air,contained within the inner chamber 232 to circulate. This is achieved bythe presence of the vanes 254 on the external surface of the drum 250.Rotation of the drum 250, and therefore of the vanes 254, causesmovement of the air and water vapour in a radial then axial, directionbetween the drum 250 and the cylindrical wall 232 a of the inner chamber232. This in turn forces the air and water vapour to circulate to theinterior of the drum 250 and, having no other exit route, the air andwater vapour then passes through the laundry articles contained withinthe drum 250 and out of the drum 250 through the perforations in thecylindrical wall 252 a. At this stage, it is advantageous if the drum250 is rotated about the axis 236 at a speed which forces the laundryarticles to be held against the cylindrical wall 252 a. This enhancesthe evaporation of water droplets retained within the textile articlesbecause, as will be appreciated, the circulating air and water vapourwill be warmed as it passes alongside the cylindrical wall 232 a of theinner chamber 232 and the circulation of the air and water vapour causesthe transfer of thermal energy from the cylindrical wall 232 a into thetextile articles which are to be dried, The presence of the vanes 254along the length of the drum 250 has the advantage that the air andwater vapour is forced to flow more uniformly through the laundryarticles than if it were simply blown into the interior of the drum 250from outside and allowed to follow the path of least resistance throughthe fabric.

[0061]FIGS. 4a and 4 b illustrate a fourth embodiment of the invention.In this embodiment, the drying apparatus is, once again, a clothes dryer300 having an outer casing 312. The outer casing 312 consists of agenerally cylindrical wall 312 a, a rear wall 312 b and a door 312 clocated opposite the rear wall 312 b. As in previous embodiments, thecylindrical wall 312 a is shaped so that a sump 314 is formed in thelower region of the outer casing 312. An outlet 316 is provided at thelowest point of the sump 314 so that condensed water can be passed to adischarge pipe 318 via a pump 320 and a non-return valve 322. The outercasing 312 delimits an outer chamber 326 which has an outlet 328incorporating a vacuum pump 330, similar to the arrangements describedabove.

[0062] An inner chamber 332 is arranged wholly within the outer chamber326. The inner chamber 332 is generally cylindrical in shape and has asubstantially cylindrical wall 332 a, a rear wall 332 b and a door 332 clocated opposite the rear wall 332 b. As previously, the doors 312 c,332 c are aligned so as to allow laundry articles to be introduced tothe interior of the inner chamber 332. The cylindrical wall 332 a isperforated for reasons which will be described below. The inner chamber332 is mounted on a shaft 334 via bearings 334 a. A motor 334 b isprovided so as to allow the inner chamber 332 to be rotated about theaxis 336.

[0063] A fan array 340 is provided radially outwardly of the innerchamber 332. The fan array 340 comprises a multiplicity of vanes 354which extend parallel to the longitudinal axis 336 of the inner chamber332. A plurality of dividing walls 356 are provided at intervals alongthe length of the vanes 354 for reasons which will be described below. Asupport wall 340a is provided at one end of the fan array 340 to allowthe fan array 340 to be supported via bearings 344 about the shaft 334.A second motor 342 is provided to enable the fan array 340 to be rotatedat relatively high speed about the axis 336. As can be seen from FIG.4b, the vanes 354 are concave in profile.

[0064] The operation of the clothes dryer 300 is similar to that ofthose described above. In order to evacuate air from the interior of theinner chamber 332, the fan array 340 is rotated at high speed (forexample 2,000 rpm). This creates a low pressure immediately outside thecylindrical wall 332 a of the inner chamber 332. Air thus passes throughthe perforations in the cylindrical wall 332 a and is expelled from theouter chamber 326 via the outlet 328. The fan array 340 speeds up as airis expelled from the outer chamber 326. The vacuum pump 330 is thenoperated in order to evacuate the inner and outer chambers 332, 326until the pressure in the inner chamber 332 has been reduced to a valueof 12-14 kPa.

[0065] During the drying process, the inner chamber 332 is rotated aboutthe shaft 334 at speeds which will allow tumbling of the laundryarticles inside the inner chamber 332 or at speeds which will hold thelaundry articles against the cylindrical wall 332 a. Most preferably,periods of rotation at different speeds will be provided sequentially ashas been outlined above. Meanwhile, the fan array 340 continues torotate at a relatively high speed (of the order of 10,000 rpm) in orderto draw air and water vapour from the interior of the inner chamber 332through the perforations in the cylindrical wall 332 a and into theouter chamber 326. The water vapour condenses in the outer chamber 326,collects in the sump 314 and, at an appropriate time, is dischargedthrough the outlet 316 and the discharge pipe 318. The dividing wails356 arranged along the length of the vanes 354 help to ensure that theflow of water vapour from the inner chamber 332 to the outer chamber 326is spread reasonably uniformly along the cylindrical wall 332 a of theinner chamber 332.

[0066] Means for heating the contents of the inner chamber 332 have beenomitted from FIGS. 4a and 4 b for the sake of clarity. However, it willbe understood that some form of heating means may be required in orderto ensure that the water contained within the inner chamber 332 willevaporate.

[0067] In order to allow heat energy to be transferred from the outerchamber 326 back into the inner chamber 332, part of the air/watervapour mixture pumped into the outer chamber 326 by the fan array 340 isallowed to circulate back into the inner chamber 332. This recirculatedgas is at an elevated temperature because of the fact that the latentheat of condensation is given off by the condensing water vapour in theouter chamber 326. The recirculation is facilitated by the previouslymentioned perforations in the cylindrical wall 332 a. Part of the heatcarried by the recirculated gas is transferred into the water stillremaining in the laundry articles located within the inner chamber 332,which facilitates continued drying by causing evaporation of the saidwater in the inner chamber 332. The ratio of air to water vapour presentin the recirculated gas, and/or the ratio of recirculated gas tocondensed water vapour, can be adjusted so as to optimise the dryingperformance of the clothes dryer 300. In order to regulate the amount ofrecirculated gas, an adjustable valve can be provided in a singleaperture in the cylindrical wall 332 a in place of the previouslymentioned perforations. The amount of air remaining in the clothes dryer300 can be adjusted by operating the vacuum pump 330 for differentperiods of time during the drying process. This in turn will affect theair to water vapour ratio within the recirculated gas.

[0068] It will be appreciated that the invention is not intended to belimited to the precise details of the embodiments described above.Firstly, the invention is. not intended to be limited to use indishwashers and tumble dryers. Other uses will be apparent to a skilledreader. Secondly, the heaters described above need not be positioned asillustrated but any arrangement which will effect the heating of theinterior of the respective inner chamber will suffice. In a furthervariation, particularly relevant to the embodiments illustrated in FIGS.2 and 3, the doors of the inner and outer chambers can be integratedinto a single, or interconnected, door assembly. Also, different valvearrangements are possible, particularly in respect of the means foremptying the apparatus. For example, the pump in the discharge pipe canbe dispensed with if the vacuum pump can be arranged to provide anexcess pressure in the outer or upper chamber. In such an arrangement, aspool valve may be provided in association with the vacuum pump topressurise the apparatus and so force the collected condensed Water outthrough the discharge pipe when the valve therein is opened.Furthermore, the illustrative temperatures and pressures are not to beregarded as limitative. Further ,modifications and variations will beapparent to a skilled reader.

1. Drying apparatus comprising a first chamber for receiving articles tobe dried and having an outlet, a second chamber having an outlet, and afan having a fan inlet and a fin outlet, the fan inlet communicatingwith the outlet of the first chamber and the fan outlet communicatingwith the second chamber, the apparatus further comprising a vacuum pumpcommunicating with the outlet of the second chamber, the arrangementbeing such that transfer of thermal energy can take place between thefirst and second chambers and means are provided for causing forcedcirculation of water vapour contained within the first chamber. 2.Drying apparatus as claimed in claim 1, wherein the first and secondchambers have at least one common wall, the or each common wall beingthermally conductive.
 3. Drying apparatus as claimed in claim 1 or 2,wherein the first chamber is located at least partially inside thesecond chamber.
 4. Drying apparatus as claimed in claim 3, wherein thefirst chamber is located wholly within the second chamber.
 5. Dryingapparatus as claimed in any one of the preceding claims, wherein the fanis arranged to discharge gas directly into the second chamber.
 6. Dryingapparatus as claimed in any one of the preceding claims, wherein thesecond chamber comprises a water-collection region having an outlet forremoving water from the second chamber.
 7. Drying apparatus as claimedin claim 6, wherein a pump is provided in the outlet of thewater-collection region.
 8. Drying apparatus as claimed in any one ofthe preceding claims, wherein the first chamber is mounted so as to berotatable about an axis and means for causing the first chamber torotate are provided.
 9. Drying apparatus as claimed in claim 8, whereinthe fan comprises an array of vanes located radially outwardly of thefirst chamber, and means for causing the array of vanes to rotate areprovided.
 10. Drying apparatus as claimed in claim 10, wherein the firstchamber has a wall which is perforated at least in a region adjacent thearray of vanes.
 11. Drying apparatus as claimed in any one of claimes 1to 7, wherein the first chamber comprises an outer housing and an innerdrum for receiving the articles to be dried, the outer housing beingmounted so as to be stationary with respect to the second chamber andthe inner drum being rotatable with respect to the outer housing. 12.Drying apparatus as claimed in claim 11, wherein the inner drumcomprises at least one vane or blade for causing circulation of air orwater vapour within the first chamber when the drum is caused to rotate.13. Drying apparatus as claimed in claim 11 or 12, wherein the innerdrum is perforated in a region adjacent the at least one vane or blade.14. Drying apparatus as claimed in any one of the preceding claims,wherein the apparatus is a clothes dryer.
 15. Drying apparatus asclaimed in any one of claimes 1 to 7, wherein the apparatus is adishwasher.
 16. Drying apparatus substantially as hereinbefore describedwith reference to any one of the embodiments shown in the accompanyingdrawings.
 17. A method of drying articles comprising the steps of: (a)placing the articles into a first chamber; (b) evacuating a significantproportion of the air from the first chamber and from a second chamber;(c) evacuating water vapour from the first chamber to the secondchamber; (d) allowing the water vapour to condense in the secondchamber; (e) transferring thermal energy from the second chamber to thefirst chamber; and (f) causing forced circulation of the air and/orwater vapour contained within the first chamber.
 18. A method as claimedin claim 17, wherein the pressure in the first chamber is reduced tobetween 10 and 20 kPa.
 19. A method as claimed in claim 18, wherein thepressure in the first chamber is reduced to substantially 12-14 kPa. 20.A method as claimed in any one of claims 17 to 19, wherein the pressurein the second chamber is reduced to between 20 and 30 kPa.
 21. A methodas claimed in claim 20, wherein the pressure in the second chamber isreduced to substantially 25 kPa.
 22. A method as claimed in any one ofclaims 17 to 21, wherein the condensed water is drained, continuously orperiodically, from the second chamber.
 23. A method as claimed in anyone of claims 17 to 22, wherein the articles are tumbled or otherwiseagitated in the first chamber during at least part of the drying method.24. A method as claimed in any one of claims 17 to 23, wherein the airand/or water vapour in the first chamber is forced to circulate throughthe articles.
 25. A method substantially as hereinbefore described withreference to any one of the embodiments shown in the accompanyingdrawings.